Automatic regeneration control for vacuum tube circuits



Feb. 13, 1934. D. w. NORWOOD AUTOMATIC REGENERATION CONTROL FOR VACUUM TUBE CIRCUITS Filed Oct. 10, 1928 Patented Feb. 13, 1934 UNITED STATES AUTOMATIC REGENERATION CONTROL FOR VACUUM TUBE CIRCUITS Donald W. Norwood, United States Army, March Field, Calif.

Application October 10, 1928. Serial No. 311,633

1 Claim.

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 O. G. 757) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates in general to an improvement in electrical circuits, and more particularly to regeneration control of vacuum tube circuits, and has for its object the provision of an automatic regeneration or oscillation control in conjunction with vacuum tube circuits for detecting or amplifying radio signals or both.

Another object if this invention is the provision of such a regeneration control which will render the receiving circuit highly sensitive for the reception of radio signals.

With the foregoing and other objects in view, the invention consists in the combination and arrangement of parts hereinafter disclosed certain embodiments of my invention being disclosed in the accompanying drawing, in which:

Fig. l is a diagrammatical showing of a tuned circuit with a regenerative circuit and a regeneration control therefor.

Fig. 2 is a modification of the device showing a parallel circuit control.

Fig. 3 is a modification showing a variation in the input circuit Fig. 4 is a modification showing a radio frequency resistor in place of a radio frequency choke.

Fig. 5 is a modification employing a series plate feed through the feedback coil and the radio frequency resistor.

Referring more particularly to the drawing, the tuned circuit is shown as comprising an inductance coil 1, a radio frequency choke coil 1 a variable tuning condenser C, a battery B, a

three electrode vacuum tube V. Thus far this constitutes the standard circuit used in conjunction with a vacuum tube for purposes of detection or amplification.

This circuit may be made to regenerate by the addition of a feedback coil, such as shown at 1 which has a variable coupling with the grid coil -1. The use of such a circuit and the advantages of regeneration for some purposes are well known. The disadvantage of applying regeneration by this method is that another control, in addition to the tuning control, is necessary, since to secure ;maximum regeneration for all frequencies in the range of the circuit the coupling between the coils 1' and 1 must be varied to suit each individual frequency. This is caused by the fact that coupling efliciency between coils 1' and 1 changes with the change of frequency, and the reactance of coil 1 changes with the change of frequency. Also after each change of regeneration control, retuning of the tuned circuit is necessary.

Another method of controlling regeneration in this circuit is by means of a variable condenser placed in series at some point in the feedback circuit. Varying the capacity of this condenser changesthe impedance of the feedback circuit and thereby gives control of regeneration for any given frequency. The same objections, however, apply to this method of control as to the variable inductance coupling method as explained above.

I have found, as a result of experiment, that with a properly designed circuit, if a throttle con denser in the feedback circuit is kept adjusted for maximum regeneration in the circuit for all frequencies in the tuning range of the circuit, and the. throttle condenser reactance for each frequency is noted and graphically plotted against frequency, that the throttle condenser reactance curve will show up as a straight line. Furthermore, whether the reactance line rises or falls with an increase in frequency, depends upon the degree of coupling between coils 1' and 1 A degree of coupling can be found at which the reactance at the throttle condenser. in the feedback circuit may be kept constant for all frequencies in the range of the circuit. Therefore, if a reactance of the proper value, which does not change with frequency, is inserted in the feedback circuit and the proper degree of coupling between coils 1' and 1 is obtained, it will be seen that the circuit will retain the desired degree of regeneration for all frequencies in the range of the circuit without further adjustment.

I therefore arrange my circuit so as to adjust preliminarily the coupling of coil 1 and l to a proper value and to provide a proper value of radio frequency resistor R at some point in the feedback circuit. In the selection of the resistor R, I have found that a fixed resistance of the grid leak type has the properties of inductance and capacity to such a slight degree as to be negligible, and therefore serves extremely well as a radio frequency resistor which does not change appreciably in value for changes in frequency in the current flowing through it. In the use of this resistor the entire circuit is found to have the property of regeneration to any predetermined degree for all frequencies within the range of the tuned circuit.

The theory underlying the operation of this circuit is that when the two coils 1 and 1 are inductively coupled, the coupling efficiency increases with an increase of frequency of alternating currents flowing in them. This means that the energy transfer from one to the other increases with an increase of frequency. Reactance of an inductance coil increases with an increase of frequency. When the proper degree of coupling between the coils 1 and 1 is obtained, it will be seen that with an increase of frequency the tendency toward increased energy transfer will be offset by the increased reactance of the feedback coil. It then remains to cut the energy input to the feedback coil to the proper level to give the desired degree of regeneration or oscillation, which is accomplished by means of the noninductive, non-capacitive resistor R. When the above mentioned conditions are fulfilled, the circuit has the predetermined degree of regeneration or oscillation for all frequencies.

While the term regeneration has been used in the description the same principles apply to furnish any desired degree of oscillation in those cases where oscillation instead of regeneration is desired.

While the description has concerned itself with the application of the proper elements to a series controlled regenerative circuit, it is possible to apply the same principle to a parallel control of a regeneration circuit as shown in Fig. 2.

My method of regeneration control has been found to be extremely accurate, making a very sensitive circuit for reception. This circuit may be used to great advantage in the detector stage of a receiving circuit.

In the operation of a circuit, such as shown, there is a possibility of other feedbacks, in addition to the major one through the inductive coupling. Since these other feedbacks are not under control and may vary with frequency, it is necessary to compensate for them in some manner. This compensation may be accomplished by the one setting for the proper coupling between coils l and 1 and the use of the proper value resistor R.

As shown in Figs. 1 and 3, in addition to the tickler coil 1 there are three other elements in the feedback circuit, viz: a choke coil or inductive reactance 1 a condenser or capacitative reactance C and a non-inductive, non-capacitative resistance R. When the values of these elements are properly chosen in relation to the operating frequency range, and the degree of coupling between the tickler 1 and 1 is correctly adjusted, smooth regeneration results. Thus, it is apparent that all three of these elements have a co-ordinated function to perform, and it may be fairly assumed as an inherent feature of the invention, that a balancing effect is exerted by resistance R against the reactance of the other two elements as the frequency of the tuned circuit changes.

As shown in Fig. 4, I may substitute a radio frequency resistor R for the radio frequency choke 1 As shown in Fig. 5, I may also employ a series plate feed through the feedback coil and the radio frequency resistor.

The essence of all of these circuits is the same and is as follows: An impedance in the plate circuit of the vacuum tube; represented in some cases by 1 an inductance, and in some cases by R, a resistance; retards a certain percentage of the radio frequency currents flowing in the circuit. This retarded radio frequency current is available to flow in the feedback circuit. The radio frequency resistor, labelled R, in the feedback circuit retards a portion of the R. F. current available in the plate circuit and lets through just the amount necessary to energize the feedback coil to the proper degree. The feedback coil also acts as a retard to the R. F. current, but this retard unlike the other two, changes appreciably with frequency. This effect is desired since the change in current flow through the feedback circuit can be made, by proper electrical coupling of feedback coil to tuned coil, to just compensate for the change in coupling efiiciency which also takes place with change of frequency. In the cases where the R. F. resistor R, is hooked in parallel to the feedback coil, the ratio of retardation of R2 (plate circuit impedance) to bypass through R, can be made such that the proper value of current is available to the feedback coil.

I claim:

In a system of radio communication, comprising a tuned oscillatory circuit and an inductance in said circuit, the combination of a feedback circuit; means in said feedback circuit for controlling regeneration or oscillations consisting of an adjustable coil having a predetermined coupling relation with the inductance; an impedance of constant value connected in series in the feedback circuit; and a non-inductive, non-capacitative fixed radio frequency resistance element in parallel with said feedback circuit to retard thefeedback of energy and compensate for loss of coupling efficiency in proportion to frequency change of said tuned circuit.

DONALD W. NORWOOD. 

